Toronto's CN Tower has a floor made entirely of glass, and more than one visitor has needed a moment before stepping onto it. For thirty-two years, from 1975 until Dubai's Burj Khalifa overtook it in 2007, this 553-metre concrete needle stood as the world's tallest freestanding structure, built, appropriately enough, by a railway company testing how far a signal could carry over a city of rising skyscrapers.

Near the top, the revolving 360 Restaurant turns slowly enough that diners barely notice the whole of Toronto, Lake Ontario included, sliding past their plates. That famous glass floor has cracked underfoot before now, to plenty of screaming and no actual falling.

VoiceMap's self-guided audio tours treat the tower less as a destination than a compass, a landmark visible from Front Street to the Rogers Centre that helps walkers get their bearings while exploring Toronto's downtown, waterfront and entertainment district on foot.